We recently demonstrated (T. Irving and D. Maughan, (1999) Biophys. J.76:A269) the first two-dimensional X-ray patterns from the Indirect Flight Muscle (IFM) in living mutant and wild type flies during tethered flight. In the present studies, (see Bhattacharya, 1999 and in preparation), we developed a chemically skinned preparation with well-preserved structure that can be used for studies that require changing the ionic milieu of the myofilaments. Once this was done, we were able to determine the concentration of Dextran (an inert high molecular weight polymer) required to restore the in vivo lattice spacing in normal and mutant flies, an essential prerequisite for interpretable muscle mechanics studies on this system. Drosophila is one of the best understood organisms genetically so these preparations enable a large parameter space of potential experiments to understand muscle function and regulation using transgenic organisms.